Streptococcus sp. infections play an important role in equine medicine all over the world, with the ability to cause severe disease of varying and often fatal symptoms in horses.
There are two key pathogenic bacterial species of Streptococcus sp. in horses:
- Streptococcus equi ssp. equi
- Streptococcus equi ssp. zooepidemicus
Strangles results from an infection of Streptococcus equi, causing upper respiratory tract inflammation, a muco-purulent nasal discharge, and inflammation of the regional lymph nodes. This infection results very quickly in the formation of an abscess (usually in the sub-mandibular area), which may be small and resolve over time, or may become a very large and open abscess, requiring appropriate treatment. Strangles is highly contagious, and horses can be carriers and shed the infection, although they themselves may show no outward clinical signs. This means that without proper preventative husbandry and a vaccination strategy, an infection could result in large outbreaks of this disease in horse populations. S. zooepidemicus is also known to cause paralysis in foals (polyarthritis) and sporadic abortions in pregnant mares.